Just finished the amp last night. After a fixing a weak solder connection on B2, I powered up the amp. I noticed a loud hum in the left channel only which was present at low volumes at first. After the tubes warmed up, the hum disappeared, so I ignored and I listened to the amp for a bit without issue.
This morning, I moved the amp to my desk, powered it up and there is a constant loud hum in the left channel again, but it won't change now regardless of volume setting. I checked resistances on all of the ground connections after the potentiometer in the signal path with 12U and they were all 0. I noticed that if I tapped the 12AU7 a bit, the hum would change slightly but then came right back. I plan later today to reheat the ground connections and pretty much everything on the left channel downstream of the potentiometer, but is there anything specific connection that I should check? Is it possible that the tube is faulty?
